A medical institution has a radiation tomographic imaging apparatus for imaging tomographic images of subjects with radiation. As such a radiation tomographic imaging apparatus, there is a PET (Positron Emission Tomography) apparatus which images a radioactive drug in an subject, for example.
Tomographic images with the PET apparatus are images when the subject is cut at certain planes, in which densities of the radioactive drug are represented by luminance. How the radioactive drug moves within the subject can be grasped by generating dynamic tomographic images picked up continuously in one inspection within a fixed period of time. Or the metabolism and accumulation in the subject of the radioactive drug can be known from static tomographic images obtained by one shooting after lapse of a fixed period of time.
The PET apparatus is used for diagnosis relating to the brain such as Alzheimer's disease. In such diagnosis, the subject is administered and injected with a drug labeled with radioisotope and binding to brain amyloid protein, and diagnosis is carried out to check the behavior within the brain of this drug.
In order to conduct a diagnosis using such tomographic images, dynamic tomographic images of the brain of the subject are acquired first. Then, an analysis is carried out on time variations within a fixed period of time of radioactive drug density in a specific site within the brain shown in the tomographic images. Such analysis enables a diagnosis based on functional images of the specific site. The functional images are a generic name for images showing various activities of the brain, which are distinguished from form images showing structures such as sulci and hollows of the brain. The tomographic images acquired at this time will be called herein dynamic PET images.
Incidentally, in conducting diagnoses with functional images, one site of tomographic images is often designated as a region of interest (ROI). An analysis is conducted using this designated ROI as a specific site. The ROI designated at this time is cerebellar cortex, for example. Since there are individual differences in the shape of brain, the shape of the cerebellar cortex is also different between individuals. Therefore, the ROI needs to be designated individually by recognizing the shape of cerebellar cortex of an individual.
So, according to a conventional construction, when designating a site of interest, reference is made to static PET images or form images enabling recognition of the ROI. The form images are static tomographic images in which the internal shape of the brain is imaged. These form images are acquired with an MRI apparatus or CT apparatus before or after imaging by the PET apparatus. The dynamic tomographic images acquired with the PET apparatus represent a distribution of densities of a radioactive drug, and not images showing the internal shape of the brain, which cannot be used for designating of the ROI.
That is, in conducting an image analysis using the PET apparatus, the conventional construction uses static PET images or form images enabling grasp of the internal shape of the brain. In that case, for setting the ROI, there are a method which sets it to the shape of the brain of an subject, and a method which converts the shape of the brain of an subject into a standard brain shape determined beforehand, and sets thereon a standard ROI determined beforehand (see Patent Document 1, for example).